It is desirable, in fact necessary in many instances, to have an apparatus permitting the shutoff and temporary abandonment of a petroleum well during the course of drilling. This operation may be required while drilling offshore as a storm approaches, or while a blowout preventor is being changed or repaired.
A prior art mechanism for shutting off a well is the Halliburton Services SSC (subsurface control) Valve, described on page 3485 of the Halliburton Services Sales and Service Catalog Number 40. The SSC Valve comprises a stinger assembly and a valve assembly, which are made up and run together into the casing on drill pipe with a packer, such as a Halliburton Services RTTS packer, described on pages 3476-3477 of the aforementioned Halliburton Services catalog. The SSC Valve is run open into the casing, the packer being set with righthand rotation at the desired depth. The drill pipe is then rotated to the left, backing off the stinger assembly from the valve assembly, to which it is threaded. As the stinger backs off, it pulls a sliding valve in the valve assembly upward, closing the SSC Valve. At a certain point during the withdrawal of the stinger, spring fingers on the sliding valve pop into a recess in the bore of the valve assembly, locking the sliding valve in the closed position, and disengaging it from the stinger, which is then pulled to the surface on the drill pipe. The packer supports the SSC Valve and the drill pipe below it until it is desired to recommence drilling, at which point the stinger assembly is run back into the valve assembly, and rotated to the right, which re-opens the sliding valve and makes up the stinger assembly with the valve assembly again. An upward pull on the pipe string then unseats the packer, and the string can then be returned to the surface or circulation re-established and drilling continued.
While the subsurface control valve of the prior art does permit shutoff of a well during drilling, it possesses several operational difficulties which significantly impede its performance and reliability. When the stinger assembly is re-inserted into the valve assembly, there is a significant initial shock even if the operator is extremely careful, due to the weight of the pipe string and stretch in the string, which makes exact calculation of the point of contact impossible. When the threaded portions of the two assemblies make contact, the force is taken by the makeup threads often causing damage. As the stinger enters the valve assembly and contacts the sliding valve, it generally orients the two assemblies with respect to one another. However, there is no assurance that the threads of the two assemblies will be accurately aligned. As a result, in some instances when the threads jam or do not mate precisely, other threaded joints in the valve assembly may be fractured due to the excess torque applied due to the jammed or misaligned threads between the two assemblies. Furthermore, there is no way to accurately control the amount of axial force applied to the threads, the force being solely a function of how much pipe weight is set down. If too much is permitted, the threads may jam, or fracture if weight is applied suddenly.